This invention relates to the use of a priming fluid in ink jet printers and in particular, to the use of an aqueous priming fluid used in conjunction with aqueous based ink jet inks in ink jet printers using ink jet printheads, such as, piezo ink jet printheads.
In a typical ink jet printer, ink is passed from a reservoir to an ink jet printhead and then is printed onto a substrate that typically is a sheet of paper, vinyl, cardboard, or a woven or a non-woven fabric. At the start of the printing process, when the dry ink jet printhead is initially filled with ink, problems often occur. The ink does not adequately wet the walls and passageways in the ink jet printhead. This is a particular problem with piezo ink jet printheads. If there is inadequate wetting of the surfaces in the printhead, air bubbles will be entrapped in the ink and, on firing of the printhead, ink will not be applied causing skips in printing and irregular printing until the ink fully wets the interior of the printing head; then the ink is applied uniformly.
There is a particular problem with printheads used in industrial applications as opposed to printheads used in desk top printers since the inks in such industrial applications are of a higher viscosity and the printheads are made of metals, such as stainless steel, nickel or aluminum, and ceramic components, that are more difficult to wet in comparison to the printheads used in desk top printer applications.
It is possible to formulate inks that will sufficiently wet the interior of a printhead and any related components; however, such inks will in general have problems maintaining their firing characteristics over a long term. Inks that wet the printhead and related components also wet the surface nozzle plate of the printhead during printing. The result is pooling or puddling of ink around the nozzle outlets which leads to misdirection of the ink drops being fired from the printhead during printing. Also, inks that are formulated to have good wetting characteristics often contain high levels of organic components and/or surfactants that are incompatible with other requirements of the ink, such as long term stability, firing consistency, and quality printing of the ink on a substrate. For these reasons, a formulation that meets all of the requirements of an aqueous ink jet ink is in general not useful as a priming fluid.
A process and a priming fluid, which is not an ink, are needed to provide a fully wetted surface in the printheads and channels and connectors and remove air and any contaminants therefrom, such as, foreign matter, polymer residue and the like. Such a process and fluid will substantially eliminate the entrapment of air, and printing will be even and uniform on the surface being printed from the start of printing and will be applicable for a typical desk top ink jet printer or a large industrial ink jet printer used, for example, to print fabrics or vinyl material using water based inks.
This invention is directed to a process for priming a passageway to a printhead and the interior of a printhead used in an ink jet printing process to remove air and contaminants therefrom, which comprises the step of passing an aqueous priming fluid through said passageway and into the interior of said printhead, wherein the aqueous priming fluid has an advancing contact angle of less than about 25 degrees and comprises the following:
about 10-90% by weight, based on the total weight of the priming fluid, of at least one polar, water miscible organic solvent having a solubility of at least about 5 parts per 100 parts of water (by weight), such as propylene glycol monopropyl ether, 2-pyrrolidone, dipropylene glycol monomethyl ether, and N-methyl pyrrolidone; and correspondingly
about 90-10% by weight, based on the total weight of the priming fluid, of water.
Optionally, the priming fluid may contain in addition one or more of the following additives: an organic water miscible solvent to reduce the freezing temperature, such as glycerol; surfactants to reduce surface tension and enhance wetting of the fluid; defoamers to reduce foaming; hydrotropes; acid or base or buffering agents to maintain the desired pH; colorants to impart color but not adequate to form an ink; polymeric additives; and biocides.
Another part of this invention is the novel priming fluid containing one or more of the above additives. Thus, in another embodiment, the priming fluid comprises:
about 0.1-10% by weight, based on the total weight of the priming fluid, of a surfactant or mixtures of surfactants, such as, a commercially available silicone based surfactant like, Silwet(copyright) L77, which is a mixture of a polyalkyleneoxide modified heptamethyltrisiloxane (84%) and allyloxypolyethyleneglycol methyl ether (16%), both based on the weight of the mixture, and
about 50-99.9% by weight of water, and preferably 90-99.9% by weight of water, based on the total weight of the priming fluid, with the remainder of the priming fluid (if any) comprising one or more common additives such as polar water miscible organic solvents, organic miscible solvents (for example, to reduce the freezing temperature), defoamers, hydrotropes, acids or bases and/or buffers, polymeric additives, biocides, colorants or fluorescent agents as mentioned above.
These and other features and advantages of the present invention will be more readily understood by those of ordinary skill in the art from a reading of the following detailed description. It is to be appreciated that certain features of the invention which are, for clarity, described above and below in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. In addition, references to in the singular may also include the plural (for example, xe2x80x9caxe2x80x9d and xe2x80x9canxe2x80x9d may refer to one, or one or more) unless the context specifically states otherwise.